1. Field of the Invention
The present invention relates to a method of laying out a foundation stirrup for a lower extremity orthosis so that the mechanical axis of the stirrup coincides with the anatomical ankle joint and to a calliper useful therein.
The laying out of a foundation stirrup involves the finding of two essential points on the stirrup: the vertical and longitudinal center lines and the mid-point between the stirrup joint holes. When these points have been located on the stirrup, measurements can be taken from the mid-point to locate exactly where the stirrup should be bent in order to fit the orthosis assembly. For patients with a varus or valgus deformity (ankle turned in or out), the deformity needs to be noted on the stirrup when measuring for the bend points in order to assist in the correction of the deformity.
2. Description of the Prior Art
There is no known prior art directly related to the mechanical or automatic measuring of a stirrup to determine its bend points or lines. Devices are known for the correction and improvement of faulty foot posture in a patient through alignment of the feet by measurement of the degree of fault found in the patient's feet, for the purpose of making a wedge for insertion into a corrective shoe; see U.S. Pat. No. 2,492,059 to G. Ogden issued Dec. 20, 1949. Stirrups and the orthotic devices for which they comprise the foundation of are, of course, known as well, see e.g. U.S. Pat. No. 3,732,861 to H. Lehneis, issued May 15, 1973.
The conventional prior art tools used to lay out a stirrup for measurement are a ruler, grease pencil and a straight edge. For a normal foot, the vertical (lateral) and longitudinal center lines are layed out with the ruler and pencil and the mid-point between the joint holes of the stirrup is thus designated. Where a varus or valgus deformity is present, the stirrup must be manually measured in this fashion so that it may be off-set to one side of the foot or the other when bent. A center hole, either at the intersection of the vertical and longitudinal center-lines, or off-set in the case of a deformity, is then drilled. In order to measure the bend points and form the stirrup, the medial lateral width of the shoe at the heel breast is measured and increased by a width of an inch. This dimension is then manually marked equally on each side of the drilled center hole. The stirrup is then transferred to a stirrup bender in order to form the stirrup bends from the measurement taken.
Laying out a stirrup in the above mentioned manner is very time consuming, tedious and often inaccurate, particularly under the pressure of a large volume of work to be completed.
If the stirrup is not laid out correctly, the following problems often arise: binding and excessive wear at the mechanical joint, rapid tiring of the patient's leg due to the muscular effort the patient must expend in trying to overcome the defective mechanical joint, and even temporary or permanent damage to the patient's limb.